Automotive Extreme driveshaft material?

Ok so ive ran into some issues figuring out what i material i should use as a driveshaft im not going to give many specs on the engine except 20,000 peak ft-lbs torque. With the transmission in the lowest gear 5:1 and the transfer case in 6:1 the output to the driveshaft is 600,000 ft-lbs of torque Calculated! You can see where im running into an issue here with the driveshafts ability to hold that much torque without breaking using driveshaft calculators i would need a driveshaft in excess of 8in diameter with 4in of wall thickness and still not have the ability to stay together. Im asking for help here on any alternatives to a driveshaft or insight on what material i should use on the driveshaft because this mud truck would look funky with a 8+inch driveshaft. Also the driveshaft will have a max rpm of 28571 rpm in the custom overdrive ratio If that will help

Staff: Mentor

Ok so ive ran into some issues figuring out what i material i should use as a driveshaft im not going to give many specs on the engine except 20,000 peak ft-lbs torque. With the transmission in the lowest gear 5:1 and the transfer case in 6:1 the output to the driveshaft is 600,000 ft-lbs of torque Calculated! You can see where im running into an issue here with the driveshafts ability to hold that much torque without breaking using driveshaft calculators i would need a driveshaft in excess of 8in diameter with 4in of wall thickness and still not have the ability to stay together. Im asking for help here on any alternatives to a driveshaft or insight on what material i should use on the driveshaft because this mud truck would look funky with a 8+inch driveshaft. Also the driveshaft will have a max rpm of 28571 rpm in the custom overdrive ratio If that will help

What kind of engine are you running that puts out that much torque? Per this wiki page, the highest torque outputs in production vehicles are the following:

Something isn't registering in my head. You have a drive shaft that will turn almost 30000 RPM? With say, a 3:1 reduction to the axle, that's 10000 axle RPM. Assuming a car tire that turns 800 rev's/mile, that would produce a speed of 350 MPH. With tall truck tires... That's quite a mud truck!

One thing to consider is that even with an engine that can produce the numbers you are quoting, the maximum the shafts will carry is limited by tire traction.

Staff: Mentor

So you have an engine that puts out more than twice the torque as is described here, with 7400 ft-lb for a top fuel dragster?

[PLAIN said:

https://en.wikipedia.org/wiki/Top_Fuel][/PLAIN] [Broken]
Measuring the power output of a top fuel engine directly is not always feasible. Certain models use a torque sensor incorporated as part of the RacePak data system. Dynamometers that can measure the output of a Top Fuel engine exist; however, the main limitation is that a Top Fuel engine cannot be run at its maximum power output for more than 10 seconds without overheating or possibly destroying itself explosively. Making such high power levels from such relatively limited displacement is a result of using very high boost levels and running at extremely high RPMs; both of these stress the internal components to a high degree, meaning that the peak power can only safely be achieved for brief periods of time, and even then only by intentionally sacrificing components. The engine power output can also be calculated based upon the car's weight and its performance. The calculated power output of these engines is most likely somewhere between 6,340 and 7,460 kW (8,500 and 10,000 hp), which is about twice as powerful as the engines installed on some modern diesel locomotives, with a torque output of approximately 10,000 newton metres (7,400 lbf·ft) and a brake mean effective pressure of 8.0–10.0 MPa (1,160–1,450 psi).

In late 2015, tests using sensors developed by AVL Racing showed peak power of over 11,000 hp (8,200 kW).

I don't think it's a criticism, so much as needing more context. Any "mud truck" as you describe it could not utilize the power that a shaft that large could carry (maybe if it weighed 100,000 pounds, and then I don't know how it reaches the speeds you mention). There's more to designing a shaft than how much torque the engine could produce in it. If there isn't enough load on the shaft (from traction), the torque would not get that high, and you'd be over-designing the shaft.

To advise you meaningfully, we'd need tire diameter, final drive reduction between the drive shaft and the axle, and vehicle weight.

OK. From the tire diameter, the radius is 32.5 inches, or 2.71 feet. I'm going to make some assumptions and work through an example of what I mean.

Assuming that one axle carries half the vehicle weight, and the coefficient of friction is 1.0 (considerably too high for mud), the maximum traction on one axle is 12,500 pounds. With a 2.71 foot tire radius, it would require 12500 x 2.71 = 33,875 ft-lb torque at the axle.

The final drive reduction I mentioned is the gear ratio between the drive shaft and the axle. Not knowing any better, I'll assume it's a 3.00:1 ratio. Then the drive shaft torque would be (33,875 ft-lb)/3.00 = 11,300 ft-lb. Much lower than could be produced by the engine and transmission you've mentioned.

Of course you need a safety factor when designing a driveshaft, to account for shock loading and unknowns. So instead of 11,300, maybe you design for 40,000 ft-lb. This method, with proper assumptions, should get you in the ballpark.

Staff: Mentor

Its a non traditional engine all i need is help with the driveshaft so can i get anymore insight Besides criticizing the engine?

I'm not criticizing the engine. I just find it hard to believe that your engine makes so much power, when the state of the art in gasoline engines seems to be currently at about 11,000 HP, and somewhere around that figure for ft-lb of torque.

Staff: Mentor

Diesel locomotive with 6600 HP. I believe the engine is about the size of your truck and probably about 8-10 times the mass of the truck. Point is: it does not seem feasible to have an engine to have the HP you mentioned and still be viable in a truck of that size.

I give up. @Ranger Mike probably knows more than all of us on this subject.

Diesel locomotive with 6600 HP. I believe the engine is about the size of your truck and probably about 8-10 times the mass of the truck. Point is: it does not seem feasible to have an engine to have the HP you mentioned and still be viable in a truck of that size.

I give up. @Ranger Mike probably knows more than all of us on this subject.

Lets assume you've not made an error. Just to put it into context. Somethong on the order of 11,000 HP is 8MW. thats the same power output as a large wind turbie. Or a high speed marine diesel engine that powers ships.

If the numbers you posted are right. Are you really surprised that your driveshafts need to be physically colossal?

I put together a table of speeds in the different gears. I hope I understood them right - I'm not familiar with a 2-speed diff with either a 32:1 or 1.2:1 option. If correct, the top speeds in each gear would range from 9.43 MPH to 168 MPH, assuming the 32:1 ratio (you can double check the numbers). As you can see, with the 1.2:1 ratio, the top speeds would range from 251 to 4500 MPH!
1st 2nd 3rd 4th 5th 6th 7th
RPM Tire Axle 5.00 2.75 1.75 1.00 0.65 0.48 0.28
7800 65 32.0 Speed (mph) 9.43 17.14 26.93 47.14 72.52 98.20 168.34
1.2 Speed (mph) 251.39 457.07 718.25 1256.93 1933.75 2618.61 4489.05

Even with the 32:1 ratio, a 168 MPH forward speed, or just spinning the wheels that fast) would most likely explode the tires. The 1.2:1 ratio would be unnecessary, unless there's more to this. I imagine spinning the components in the driveline this fast, with the torque your are talking about, will be a major issue. And you won't have enough power to exercise most of the gears fully - especially in the mud.

I put together a table of speeds in the different gears. I hope I understood them right - I'm not familiar with a 2-speed diff with either a 32:1 or 1.2:1 option. If correct, the top speeds in each gear would range from 9.43 MPH to 168 MPH, assuming the 32:1 ratio (you can double check the numbers). As you can see, with the 1.2:1 ratio, the top speeds would range from 251 to 4500 MPH!
1st 2nd 3rd 4th 5th 6th 7th
RPM Tire Axle 5.00 2.75 1.75 1.00 0.65 0.48 0.28
7800 65 32.0 Speed (mph) 9.43 17.14 26.93 47.14 72.52 98.20 168.34
1.2 Speed (mph) 251.39 457.07 718.25 1256.93 1933.75 2618.61 4489.05

Even with the 32:1 ratio, a 168 MPH forward speed, or just spinning the wheels that fast) would most likely explode the tires. The 1.2:1 ratio would be unnecessary, unless there's more to this. I imagine spinning the components in the driveline this fast, with the torque your are talking about, will be a major issue. And you won't have enough power to exercise most of the gears fully - especially in the mud.

I have used multiple gear calculators and with the 32:1 ratio im still debating on dropping the .28 gear ratio, the 2 speed diff is going to have to be a custom order along with tires due to the extreme nature of this build so axletech and which ever tire company i pick is going to have a challenge. I have linked a photo album of the calculators with the info imputed. http://m.imgur.com/yU5xUab,EesuWAq,1oTLSWj,rLYBMN1 The 1.25 gearing is only for wheel spin in the mud nothing else

I have no idea what you are trying to achieve with this. From an engineering approach, it just feels a bit 'off'.

Suspect engine outputs asside, the slection of gear ratios, transfer box and FDR. Just doesnt feel right. The selection of a super short and super long FDR is just a bit bizzare tbh.

The truck is going to be a sled pull truck and a mud truck yea i know the specs and stuff sound off ive had that said before. The transfer case is an atlas ll 6.0 and the transmission is most likely going to be from liberty gears and custom made they have made transmissions for record breaking vehicles. The ratios picked are just from personal preference and pull of each gear stuff like that. The reason i picked 32:1 was mainly just pulling, the 1.25:1 is just for competition mudding for the wheel rpm. When i contact Axletech about engineering a 2 speed diff i may see if they can do a 3 speed diff for a axle ratio more streetable (may ask about a hydro or pneumatic extending axle for onroad compact for street legal width and extendable for offroad. Im open to suggestions and ideas about the build drivetrain wise :)